Means and method for purging a hydraulic system



R. C. BEAVER Oct. 27, 1964 MEANS AND METHOD FOR PURGING A HYDRAULIC SYSTEM Filed DeO. 26, 1961 e mm T M Vl m5 M N. R m I6 m m .T i A fx f FIG.|

United States Patent O 3,154,087 MEANS AND METHOD FOR PURGING A HYDRAULIC SYSTEM Richard C. Beaver, Inglewood, Calif., assgnor to Quadrant Engineering Corporation, Gardena, Calif., a corporation of California Filed Dec. 26, 1961, Ser. No. 161,907 11 Claims. (Cl. 137-15) This invention relates to a means and method for purging a hydraulic system and more particularly to a means and process for purging hydraulic systems of gas, in most cases air, land to completely till the entire system with a hydraulic liquid.

Many airplanes and missiles and other machinery have complex hydraulic control systems and in many instances it is impractical to make complete provisions for bleeding the air from all dead-end pockets and chambers. Moreover, it is almost impossible to bleed the air from small packings, 'O-ring grooves, threads, etc. When air is present in these hydraulic systems, it results in a very spongy action of components actuated by the system. A common example of this is to watch an airplane lower its landing gear. When there is a jerky motion of the landing gear, air is indicated in the hydraulic system.

Another example of hydraulic systems is the application in a hydraulic controlled tracer machine tool, such as a duplicating mill. Such mills have intricate servo hydraulic system which have to control movement with very small tolerances, for example, in thousandths of inches. In these servo systems, any air in the hydraulic system makes it impossible to hold the close tolerances required; however, in many cases it is impractical to make provisions in the hydraulic system to bleed the air from all of the dead-end pockets.

This invention, n the other hand, provides a new and improved means and process for purging a hydraulic system to eliminate all the air from pockets and traps thereof4 by first purging the hydraulic system with a condensible saturated vapor, with suitable properties such as Freon which has the ability to iirst mix with and dilute the air in the pockets and traps. As more purging takes place, the diluted air vapor mixture is replaced with vapor alone. The entire system is then lled with vapor, after which an open end thereof is shut off and the vapor is continued to be introduced until the vapor reaches its vapor pressure. At this point, hydraulic liquid is pumped into the system and as the hydraulic liquid pressure is increased the vapor condenses back to a liquid until the complete system is lled with a liquid. A In la closed system, the hydraulic fluid returns to the reservoir Where the condensed vapor may completely or partly evaporate, or flash, out of the hydraulic liquid when at atmospheric pressure.

It is therefore the primary object of this invention to provide a new and improved means for purging a hydraulic system wherein the air held in dead-end pockets and traps of the system is completely removed from the system. i

It is another object of this invention to provide a new and improved process by which the air caught in pockets and traps of the hydraulic system is completely removed therefrom. Y

It is yet another object of this invention to provide a new and improved means and process for purging a hydraulic system in which the purging vapor is subsequently used to remove any air trapped in pockets land traps of the hydraulic system.V

A further object of this invention is to provide a new and improved means and process for purging a hydraulic system which is effective to completely purge the system at a pressure substantially smaller than the normal operative pressure of the hydraulic system.

A general object of this invention is to provide la new and improved means and process for purging a hydraulic system which overcomes disadvantages of prior means and methods heretofore intended to accomplish generally similar purposes.

These and other objects of this invention will be more apparent from the following detailed description, drawings, and appended claims.

In the drawings:

FIGURE 1 is a schematic flow diagram illustrating the means and method of this invention as applied to an exemplary hydraulic system, with parts broken Iaway for greater clarity;

FIGURE 2 is an enlarged, vertical, cross-sectional, end diagrammatic view showing a portion of the system of FIGURE 1 in greater detail and illustrating a primary step of this invention;

FIGURE 3 is a vieW, similiar to FIGURE 2, showing a secondary step of this invention;

FIGURE 4 is a view similar to FIGURES 2 and 3, illustrating a final step as taught by this invention;

FIGURE 5 is a schematic representation of a Valve means of FIGURE l in one position; and

FIGURE 6 is a schematic representation of the valve means of FIGURES l and 5 in another position.

Referring in detail to the drawings, there is shown by way of illustration, but not of limitation, a hydraulic system shown diagrammatically for exemplifying the means and method for purging a hydraulic system of this invention and generally designated by the numeral 410. The hydraulic system 10, as shown herein, comprises a reservoir 11 adapted to contain a hydraulic fluid vented to atmospheric pressure as by its open top 12 a conduit 13 by which iluid is drawn out of the reservoir and a return conduit 14 for circulating the hydraulic uid referred to by the numeral 15.

The inlet conduit 13 is connected to the inlet end 16 of a pump 17 selectively driven as by a motor 18, there being la check valve 19 assuring flow of the hydraulic fluid 15 from the reservoir 11 through the conduit 13 to the inlet 16 of the pump 17. A T connector 21 is provided in the conduit 13 for connecting the conduit to a means for purging the hydraulic system 10 With a condensible saturated vapor 22, such means including a storage tank 23 for storing the purging vapor and a needle valve 24 controlling flow of the vapor 22 into the conduit 13 for communication with the inlet 16 of the pump 17 The Vsystem 10 may further include Various elements normally associated with hydraulic systems, such as a conduit 26 connected to the outlet of the pump 17, a check valve 27 controlling the flow of the fluid within the conduit 26 so as to flow in a direction away from the pump 17 yand to a pressure switch generally indicated by the numeral 28, a pressure gauge 29 for measuring'the pressure of fluid within the conduit 26 and control valve 31 for controlling the ow of iluid from the conduit 26 to selective sides of a hydraulic cylinder generally designated by the numeral 32 which hlas, for example, conduits 33 and 34 connected to the control valve 31 and communicating with opposed sides of the interior of the cylinder 32 so as to induce movement to a piston 36, movable within the cylinder 32 and having a piston rod 37 for transmitting linear axial movement of the piston 36 to a device (not shown) connected to the outer end of the piston rod 37, in accordance with the positioning of the control valve 31.

The return conduit 14 is provided with a shut off valve 38 which is manually operable for selectively closing and opening the conduit 14 for selectively permitting iiow of uid through the conduit 14 into the reservoir 11 or building up the pressure within the system when the valve 38 is closed.

The tank 23 is charged with a purging vapor under pressure which is in a gaseous state or is optionally in liquid form in the storage tank to take the form of a gas when released therefrom. Many types or combinations of vapor and liquid stlate substances can be used for purging the hydraulic system and contained in the pressure rise container 23. However, in practice, the vapor selected preferably possesses suitable properties such as: having a vapor pressure below the operating pressure of the hydraulic system; be compatible with the hydraulic liquid in the hydraulic system; be compatible with the components comprising the hydraulic system, i.e., one which will not attack or corrode the components of the system; and have the properties to completely or partly ilash out of the hydraulic liquid in the reservoir when vented to atmosphere as will be hereinafter described. A satisfactory vapor useable in this system is Freon-IZ which substantially meets the above referred to prerequisites.

In prior purging means yand methods, complete purging of the system cannot be completely and satisfactorily purged inasmuch as air is trapped within dead-end pockets and chambers, small packings, O-ring grooves, threads, etc., causing a spongy and jerky motion when in the components of the hydraulic system. Such air is indicated in the component parts of the system in FIGURES 1 and 2, such as 1an upper conical cavity 39 within the body of the check valve 27, the Bourdon tube 41 0f the pressure switch 28, a similar Bourdon tube 42 in the pressure gauge 29, an upper space on the interior of the cylinder 32, all such spaces being indicated by the numeral 39. Also in this system, air is usually trapped in upper spaces surrounding movable stems, and other chambers and O-ring grooves of the component parts of the system.

In accordance with this invention, the system is primarily purged by admitting the vapor from the storage tank 23 through the needle valve 24 rinto the conduit 13 to be pumped by the pump 17 into the system wherein the Vapor has the ability to rst mix with and dilute the air trapped .in the various spaces mentioned. Purging is continued and, as more purging takes place, the diluted air vapor mixture is replaced with pure vapor as indicated cated by lthe numeral 22 and as exemplified in FIGURE 3.

When the entire system l10 is iilled with vapor 22, the open end 44 of the conduit 14 is shut olf by the valve 38 and the vapor is continued to be introduced until the vapor finally reaches its vapor pressure (for Freon-12, the pressure equals 70.12 p.s.i.g. at 70 F.). At this point, hydraulic liquid is pumped into the system and as the hydraulic liquid pressure is increased, the vapor condenses back into a liquid until the complete system 10 is filled with a liquid (at a predetermined pressure above the vapor pressure of the vapor used for purging the system). In the flow system, the hydraulic liquid returns to the reservoir by opening 'the valve 38 Where the condensed vapor may completely or partially flash out of the hydraulic liquid 15 when at atmospheric pressure. At the final stage, the system is operated by the pump 17 driven by the motor 18 a-t the operating pressure of the hydraulic system and because the vapor pressure is below such an operating pressure, the vapor element remains in liquid form until flashed out in the reservoir 11. It 'is apparent that the condensation of the vapor could take place at a pressure above the vapor pressure but below the operating pressure of the system and that after complete purging, the operating pressure could be of any selected magnitude compatible with the system.

By this means, the air is substantially completely removed from the aforementioned pockets and air traps in the system and is replaced by first the vapor, wherein the vapor is first mixed with the air in gaseous state and then replaced by the vapor, after which the vapor is condensed into liquid state to mix with the hydraulic fluid and subsequently be carried out of the system for evaporation in the reservoir which is vented to atmosphere.

While there is herein shown and described what is conceived to be the most practical and preferred embodiment of this invention, it is recognized that departures may be made therefrom within the scope of this invention which is not limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices.

What is claimed as new and desired to secure by Letters Patent is:

1. A process for purging a hydraulic system comprising steps of:

purging the hydraulic system with a condensible vapor other than air until the air in the system is replaced by the said vapor;

pumping hydraulic fluid into said system at a pressure sufficient to condense said vapor to a liquid which mixes with said hydraulic iiuid; and

replacing said mixture of the liquefied vapor and hydraulic iluid with hydraulic fluid.

2. A process for purging a hydraulic system comprising steps of:

purging the hydraulic system with a condensible saturated vapor other than air until the air in the system is replaced by the said vapor;

pressurizing said system by introducing additional vapor to said system to a pressure at which the further application of pressure will effect condensation of the vapor;

pumping hydraulic fluid into said system at a pressure sufficient to condense said vapor to a liquid which mixes with said hydraulic fluid; replacing said mixture of the liquefied vapor and hydraulic uid with hydraulic fluid; and

venting said replaced mixture to atmosphere so as to liash out the liquefied vapor from said mixture.

3. A process as defined in claim 2, wherein said purging vapor is non-corrosive to the components of the hydraulic system.

4. A process as defined in claim 2, wherein said purging vapor is `condensible at a pressure equal to or substantially less than the operating pressure of the hydraulic system.

5. A process as defined in claim 2, wherein said purging vapor is Freon, having a vapor pressure of 70.12 p.s.i.g. at 70 F.

6. A means for ing:

an inlet conduit and a return conduit for said hydraulic system;

means for purging the hydraulic system with a condensible saturated vapor so as to mix with air pocketed in portions of the system and Vdiluting the air to a point at which the diluted air is replaced with said vapor;

said purging means comprising a source of said saturated vapor connected with said system through valve means;

a reservoir containing hydraulic fluid at atmospheric pressure and connecting with the inlet and return conduits of said system; and

means for pumping hydraulic iluid from said reservoir into the system at a pressure at which the vapor in said system condenses into a liquid thereby filling the system with a mixture of liquefied purging vapor and hydraulic fluid, said mixture of liqueed purging vapor and hydraulic fluid being pumped out of said system and into said reservoir in response to pumping of said hydraulic uid into said system so as to flash said liquefied vapor out of said mixture of liqueed purging vapor and hydraulic liuid when vented -to atmospheric pressure in said reservoir.

purging a hydraulic system compris- E* d 7. A means for purging a hydraulic system as defined in claim 6, wherein said means for pumping hydraulic fluid from said reservoir into said system, so as to liquefy said vapor, pressurizes said system to a pressure below the operating pressure of the hydraulic system.

8. A means for purging a hydraulic system as dened in claim 6, wherein said liquefied vapor gas vaporizes at asmospheric pressure in said reservoir.

9. A means for purging a hydraulic system as defined in claim 6, wherein said purging vapor is Freon having a vapor pressure of 70.12 p.s.i.g. at 70 F.

10. A means for purging a hydraulic system as defined in claim 6 having second valve means in said outlet conduit adjacent said reservoir for preventing ow back to said reservoir, and third valve means for closing the end of said return conduit.

11. A means for purging a hydraulic system comprisan inlet conduit and a return conduit for said hydraulic system;

means for purging the hydraulic system with a condensible saturated vapor so as to mix with air pocketed in portions of the system and diluting the air to a point at which the diluted air is replaced with said Vapor;

said purging means comprising a source of said saturated vapor connected with said system through valve means;

a reservoir containing hydraulic tluid and connecting with the inlet conduit of said system;

means for pumping hydraulic uid from said reservoir into the system at a pressure at which the vapor in said system condenses into a liquid thereby lling the system with a mixture of liquefied purging vapor and hydraulic fluid, said mixture of liquefied purging Vapor and hydraulic fluid being pumped out of said system in response to pumping of said hydraulic fluid into said system.

No references cited. 

1. A PROCESS FOR PURGING A HYDRAULIC SYSTEM COMPRISING STEPS OF: PURGING THE HYDRAULIC SYSTEM WITH A CONDENSIBLE VAPOR OTHER THAN AIR UNTIL THE AIR IN THE SYSTEM IS REPLACED BY THE SAID VAPOR; PUMPING HYDRAULIC FLUID INTO SAID SYSTEM AT A PRESSURE SUFFICIENT TO CONDENSE SAID VAPOR TO A LIQUID WHICH MIXES WITH SAID HYDRAULIC FLUID; AND REPLACING SAID MIXTURE OF THE LIQUEFIED VAPOR AND HYDRAULIC FLUID WITH HYDRAULIC FLUID. 